Glissando and Horizontal Frames and System breaks
It is my understanding that the correct way to implement "ragged right" in MuseScore is to add a Horizontal Frame at the end of the first staff and stretch it until it looks right. Next add a System Break to the Frame.
This works great!
However, if the last thing in the first staff was a glissando, the gliss will stretch to the end of the Horizontal Frame and not to the end of its parent measure. See the attached image.